Development of nitrogen doped carbonaceous materials, especially graphene (Gr) with or without metal becomes a well known strategy to replace the platinum based catalysts in the energy storage and conversion devices. Graphene with high surface area (˜2650 m2 g−1), high mechanical stability and high electron mobility etc. plays a vital role as a support and/or catalyst in the energy conversion devices. Being a zero band-gap material, it is necessary to tune the band gap of Graphene to facilitate its application in photovoltaics and optoelectronics. This can be achieved practically by the conversion of two dimensional Graphene into graphene nano ribbons (GNRs) and zero dimensional graphene quantum dots (GQDs) due to their quantum confinement and edge effects.
The recent efforts are intensively focused on the preparation of GQDs by bottom-up (refers to synthesis of GQDs by chemical carbon-carbon coupling reaction) and top-down (refers to cutting of Gr sheets into the GQDs) methods for different applications. Most recent reports demonstrated the nitrogen doped graphene quantum dots (NGQDs) as a non-Pt oxygen reduction reaction (ORR) catalyst. Although, the aforementioned reports are effective for the preparation of GQDs, the yield of these GQDs has to be increased for practical application. Moreover, in all these cases, hazardous concentrated acids have been employed to cut down the carbon source into the GQDs and excluded its resulting parent material (i.e. carbon source). Hence, an efficient and environmentally benign method for the preparation of GQDs with better yield is highly desirable.
Further, porous graphene (pGr) has also gained much attention recently in the field of nano electronics as similar to Graphene. Interestingly, the band gap of the Graphene can be tuned as similar to the band gap of TiO2 (3.2 eV) by making holes on Graphene.
Recently, the inventors group has demonstrated a versatile method for drilling nano holes on graphene assisted by pre-formed Fe2O3 nanoparticles and conversion of the latter to Fe3C through carbon spillover from Graphene. Inclusion of multi carbon vacancy along the pore openings of the two dimensional Graphene could be utilized for imparting ORR activity in the system through effective nitrogen doping.
However, the method proposed by the inventor has limitations like controlling the sizes of the pores within few nanometers and maintaining the pore distribution homogeneously throughout the surface of Graphene and reducing the wastage in the process.
Considering this long standing need of the prior art, the inventors have now come up with an environmentally friendly process without any wastage of carbonaceous material which gives the nanoporous graphene without any metal contamination and extensive damage to the Graphene framework, utilizing mild reagents and reaction conditions.